Planetary gear train of automatic transmission for vehicle

ABSTRACT

A planetary gear train of an automatic transmission for a vehicle may include a first planetary gear set, a second planetary gear set, a third planetary gear set, a fourth planetary gear set, an input shaft, an output shaft disposed in parallel with the input shaft, a first connecting member, a second connecting member, a third connecting member, a fourth connecting member, a fifth connecting member, a sixth connecting member connected to the input shaft selectively, a seventh connecting member engaged with the second connecting member, an eighth connecting member directly connected with the output shaft, and transfer gears connected with the connecting members.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority to Korean Patent Application No. 10-2016-0013648, filed Feb. 3, 2016, the entire contents of which is incorporated herein for all purposes by this reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to an automatic transmission for a vehicle.

Description of Related Art

Recent increases in oil prices are triggering stiff competition in enhancing fuel consumption of a vehicle.

In this sense, research on an automatic transmission has been performed to simultaneously provide better drivability and fuel consumption by achieving more shift stages.

However, in order to achieve more shift stages for an automatic transmission, the number of parts is typically increased, which may deteriorate installability and/or power flow efficiency and may increase production cost, and weight.

Therefore, in order to maximally enhance fuel consumption of an automatic transmission having more shift stages, it is important for better efficiency to be derived by a smaller number of parts.

In this respect, an eight-speed automatic transmission has been recently introduced, and a planetary gear train for an automatic transmission enabling more shift stages is under investigation.

An automatic transmission of eight or more shift-stages typically includes three to four planetary gear sets and five to six control elements (frictional elements), and may easily become lengthy, thereby deteriorating installability.

In this regard, disposing planetary gear sets in parallel or employing dog clutches instead of wet-type control elements has been attempted. However, such an arrangement is not widely applicable, and using dog clutches may easily deteriorate shift-feel.

In addition, a recent eight-speed automatic transmission typically shows a gear ratio span in a level of 6.5 to 7.5, which requires improvement for better fuel consumption.

Thus, shortening a length of an automatic transmission without deteriorating performance is beneficial.

The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.

BRIEF SUMMARY

Various aspects of the present invention are directed to providing a planetary gear train of an automatic transmission for a vehicle having advantages of realizing at least nine forward speeds and at least one reverse speed by a combination of four planetary gear sets, two external gears and six control elements, thereby providing improvement of power delivery performance and fuel consumption and improving installability by reducing a length.

In addition, various aspects of the present invention are directed to providing a planetary gear train of an automatic transmission for a vehicle having a wide available range of varying gear teeth of transfer gears, enabling easily obtaining optimum gear ratios for respective vehicles, thereby improving power delivery performance and fuel consumption.

According to various aspects of the present invention, a planetary gear train of an automatic transmission for a vehicle may include a first planetary gear set including first, second, and third rotation elements, a second planetary gear set including fourth, fifth, and sixth rotation elements, a third planetary gear set including seventh, eighth, and ninth rotation elements, a fourth planetary gear set including tenth, eleventh, and twelfth rotation elements, an input shaft mounted with the first and second planetary gear sets at an external circumference of the input shaft, an output shaft disposed in parallel with the input shaft and mounted with the third and fourth planetary gear set on external circumference of the output shaft, a first connecting member connected with the first rotation element, a second connecting member interconnecting the second rotation element and the fifth rotation element, a third connecting member interconnecting the third rotation element and the fourth rotation element, a fourth connecting member connected with the sixth rotation element, a fifth connecting member interconnecting the seventh rotation element and the tenth rotation element, a sixth connecting member connecting the eighth rotation element and the twelfth rotation element and connected to the input shaft selectively, a seventh connecting member connected with the ninth rotation element and engaged with the second connecting member, an eighth connecting member connected with the eleventh rotation element and directly connected with the output shaft, and transfer gears connected with the connecting members.

The first connecting member may be selectively connectable with at least one of the input shaft and a transmission housing, the third connecting member may be selectively connectable with the input shaft, the fourth connecting member may be selectively connectable with the transmission housing, and the fifth connecting member may be selectively connectable with the transmission housing.

The first planetary gear set may include a first sun gear as the first rotation element, a first planet carrier as the second rotation element, and a first ring gear as the third rotation element, the second planetary gear set may include a second sun gear as the fourth rotation element, a second planet carrier as the fifth rotation element, and a second ring gear as the sixth rotation element, the third planetary gear set may include a third sun gear as the seventh rotation element, a third planet carrier as the eighth rotation element, and a third ring gear as the ninth rotation element, and the fourth planetary gear set may include a fourth sun gear as the tenth rotation element, a fourth planet carrier as the eleventh rotation element, and a fourth ring gear as the twelfth rotation element.

On the input shaft, the first planetary gear set may be disposed toward an engine side and the second planetary gear set may be disposed at an opposite side to the first planetary gear set, and on the output shaft, the fourth planetary gear set may be disposed toward an engine side and the third planetary gear set may be disposed at an opposite side to the fourth planetary gear set.

On the input shaft, the second planetary gear set may be disposed toward an engine side and the first planetary gear set may be disposed at an opposite side to the second planetary gear set, and on the output shaft, the fourth planetary gear set may be disposed toward an engine side and the third planetary gear set may be disposed at an opposite side to the fourth planetary gear set.

The transfer gears may include a first transfer gear disposed between the second connecting member and the seventh connecting member, and a second transfer gear disposed between the input shaft and the sixth connecting member.

The planetary gear train may further include a first clutch disposed between the input shaft and the first connecting member, a second clutch disposed between the second transfer gear and the sixth connecting member, a third clutch disposed between the input shaft and the third connecting member, a first brake disposed between the first connecting member and the transmission housing, a second brake disposed between the fourth connecting member and the transmission housing, and a third brake disposed between the fifth connecting member and the transmission housing.

The planetary gear train may further include a first clutch disposed between the input shaft and the first connecting member, a second clutch disposed between the input shaft and the second transfer gear, a third clutch disposed between the input shaft and the third connecting member, a first brake disposed between the first connecting member and the transmission housing, a second brake disposed between the fourth connecting member and the transmission housing, and a third brake disposed between the fifth connecting member and the transmission housing.

According to various aspects of the present invention, a planetary gear train of an automatic transmission for a vehicle may include a first planetary gear set including first, second, and third rotation elements, a second planetary gear set including fourth, fifth, and sixth rotation elements, a third planetary gear set including seventh, eighth, and ninth rotation elements, a fourth planetary gear set including tenth, eleventh, and twelfth rotation elements, an input shaft mounted with the first and second planetary gear sets at an external circumference of the input shaft, and an output shaft disposed in parallel with the input shaft and mounted with the third and fourth planetary gear set on an external circumference of the output shaft, in which the first rotation element may be selectively connectable with at least one of the input shaft and a transmission housing, the second rotation element may be directly connected with the fifth rotation element, the third and fourth rotation elements may be directly connected to each other and selectively connectable with the input shaft, the seventh and tenth rotation elements may be directly connected to each other and selectively connectable with the transmission housing, the eighth and twelfth rotation elements may be directly connected to each other and connected with the input shaft selectively, the ninth rotation element may be connected with the fifth rotation element, and the eleventh rotation element may be directly connected with the output shaft.

On the input shaft, the first planetary gear set may be disposed toward an engine side and the second planetary gear set may be disposed to an opposite side of the engine side, and on the output shaft, the fourth planetary gear set may be disposed toward an engine side and the third planetary gear set may be disposed to an opposite side of the engine side.

On the input shaft, the second planetary gear set may be disposed toward an engine side and the first planetary gear set may be disposed to an opposite side of the engine side, and on the output shaft, the fourth planetary gear set may be disposed toward an engine side and the third planetary gear set may be disposed to an opposite side of the engine side.

The fifth rotation element may be connected with the ninth rotation element through a first transfer gear, and the input shaft may be connected with the twelfth rotation element selectively through a second transfer gear.

The planetary gear train may further include a first clutch selectively connecting the input shaft and the first rotation element, a second clutch selectively connecting the second transfer gear and the twelfth rotation element, a third clutch selectively connecting the input shaft and the fourth rotation element, a first brake selectively connecting the first rotation element to the transmission housing, a second brake selectively connecting the sixth rotation element to the transmission housing, and a third brake selectively connecting the seventh rotation element to the transmission housing.

The planetary gear train may further include a first clutch selectively connecting the input shaft and the first rotation element, a second clutch selectively connecting the input shaft and the second transfer gear, a third clutch selectively connecting the input shaft and the fourth rotation element, a first brake selectively connecting the first rotation element to the transmission housing, a second brake selectively connecting the sixth rotation element to the transmission housing, and a third brake selectively connecting the seventh rotation element to the transmission housing.

According to a planetary gear train of various embodiments of the present invention, planetary gear sets are dividedly arranged on input and output shafts disposed in parallel, thereby reducing a length and improving installability.

According to a planetary gear train of various embodiments of the present invention, at least eight forward speeds and at least one reverse speed are realized by employing two transfer gears in addition to a combination of planetary gear sets, thereby providing a wide range of varying gear teeth so as to easily achieve optimum gear ratio and to easily comply with required performance for respective vehicles.

In addition, according to a planetary gear train of various embodiments of the present invention, a gear ratio span of more than 11.0 may be achieved while realizing at least nine forward speeds and at least one reverse speed, thereby maximizing an engine driving efficiency.

Furthermore, the linearity of step ratios of shift stages is secured while multi-staging the shift stages with high efficiency, thereby making it possible to improve drivability such as acceleration before and after a shift, an engine speed rhythmic sense, and the like.

It is understood that the term “vehicle” or “vehicular” or other similar terms as used herein is inclusive of motor vehicles in general such as passenger automobiles including sports utility vehicles (SUV), buses, trucks, various commercial vehicles, watercraft including a variety of boats and ships, aircraft, and the like, and includes hybrid vehicles, electric vehicles, plug-in hybrid electric vehicles, hydrogen-powered vehicles and other alternative fuel vehicles (e.g., fuel derived from resources other than petroleum). As referred to herein, a hybrid vehicle is a vehicle that has two or more sources of power, for example, both gasoline-powered and electric-powered vehicles.

The methods and apparatuses of the present invention have other features and advantages which will be apparent from or are set forth in more detail in the accompanying drawings, which are incorporated herein, and the following. Detailed Description, which together serve to explain certain principles of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a planetary gear train according to various embodiments of the present invention.

FIG. 2 is an operational chart for respective control elements at respective shift-stages in a planetary gear train according to various embodiments of the present invention.

FIG. 3 is a schematic diagram of a planetary gear train according to various embodiments of the present invention.

FIG. 4 is a schematic diagram of a planetary gear train according to various embodiments of the present invention.

It should be understood that the appended drawings are not necessarily to scale, presenting a somewhat simplified representation of various features illustrative of the basic principles of the invention. The specific design features of the present invention as disclosed herein, including, for example, specific dimensions, orientations, locations, and shapes will be determined in part by the particular intended application and use environment.

DETAILED DESCRIPTION

Reference will now be made in detail to various embodiments of the present invention(s), examples of which are illustrated in the accompanying drawings and described below. While the invention(s) will be described in conjunction with exemplary embodiments, it will be understood that the present description is not intended to limit the invention(s) to those exemplary embodiments. On the contrary, the invention(s) is/are intended to cover not only the exemplary embodiments, but also various alternatives, modifications, equivalents and other embodiments, which may be included within the spirit and scope of the invention as defined by the appended claims.

FIG. 1 is a schematic diagram of a planetary gear train according to various embodiments of the present invention.

Referring to FIG. 1, a planetary gear train according to various embodiments of the present invention includes an input shaft IS, an output shaft OS, first, second, third, and fourth planetary gear sets PG1, PG2, PG3, and PG4, two transfer gears TF1 and TF2 and control elements of three clutches C1, C2, and C3 and three brakes B1, B2, and B3.

The input shaft IS is an input member and the torque from a crankshaft of an engine is input into the input shaft IS, after being torque-converted through a torque converter.

The output shaft OS is an output member, and, arranged in parallel with the input shaft IS, outputs a shifted driving torque to a drive shaft through a differential apparatus.

The first and second planetary gear sets PG1 and PG2 are arranged at external circumference of the input shaft IS and form a main shifting portion, where the first planetary gear set PG1 is arranged toward an engine side, and the second planetary gear set PG2 is arranged toward an opposite side of the engine.

The third, fourth planetary gear set PG3 and PG4 is arranged at external circumference of the output shaft OS disposed in parallel with the input shaft IS and forms an auxiliary shifting portion, where the fourth planetary gear set PG4 is arranged toward an engine side, and the third planetary gear set PG3 is arranged toward an opposite side of the engine.

The first planetary gear set PG1 is a single pinion planetary gear set, and includes a first sun gear S1, a first planet carrier PC1 that supports first pinion P1 externally engaged with the first sun gear S1, and a first ring gear R1 that is internally engaged with the first pinion P1. The first sun gear S1 acts as a first rotation element N1, the first planet carrier PC1 acts as a second rotation element N2, and the first ring gear R1 acts as a third rotation element N3.

The second planetary gear set PG2 is a single pinion planetary gear set, and includes a second sun gear S2, a second planet carrier PC2 that supports second pinion P2 externally engaged with the second sun gear S2, and a second ring gear R2 that is internally engaged with the second pinion P2. The second sun gear S2 acts as a fourth rotation element N4, the second planet carrier PC2 acts as a fifth rotation element N5, and the second ring gear R2 acts as a sixth rotation element N6.

The third planetary gear set PG3 is a single pinion planetary gear set, and includes a third sun gear S3, a third planet carrier PC3 that supports third pinion P3 externally engaged with the third sun gear S3, and a third ring gear R3 that is internally engaged with the third pinion P3. The third sun gear S3 acts as a seventh rotation element N7, the third planet carrier PC3 acts as an eighth rotation element N8, and the third ring gear R3 acts as a ninth rotation element N9.

The fourth planetary gear set PG4 is a single pinion planetary gear set, and includes a fourth sun gear S4, a fourth planet carrier PC4 that supports fourth pinion P4 externally engaged with the fourth sun gear S4, and a fourth ring gear R4 that is internally engaged with the fourth pinion P4. The fourth sun gear S4 acts as a tenth rotation element N10, the fourth planet carrier PC4 acts as a eleventh rotation element N11, and the fourth ring gear R4 acts as a twelfth rotation element N12.

In the arrangement of the first, second, third, and fourth planetary gear sets PG1, PG2, PG3, and PG4, the second rotation element N2 is directly connected with the fifth rotation element N5, the third rotation element N3 is directly connected with the fourth rotation element N4, the seventh rotation element N7 is directly connected with the tenth rotation element N10, and the eighth rotation element N8 is directly connected with the twelfth rotation element N12, by eight connecting members TM1 to TM8.

The eight connecting members TM1 to TM8 are hereinafter described in detail.

The first connecting member TM1 is connected with the first rotation element N1 (first sun gear S1), and selectively connectable with the input shaft IS or the transmission housing H thereby selectively acting as an input element or selectively acting as a fixed element.

The second connecting member TM2 interconnects the second rotation element N2 (first planet carrier PC1) and the fifth rotation element N5 (second planet carrier PC2).

The third connecting member TM3 interconnects the third rotation element N3 (first ring gear R1) and the fourth rotation element N4 (second sun gear S2), and is selectively connectable with the input shaft IS, thereby selectively acting as an input element.

The fourth connecting member TM4 is connected with the sixth rotation element N6 (second ring gear R2), and selectively connectable with the transmission housing H, thereby selectively acting as a fixed element.

The fifth connecting member TM5 interconnects the seventh rotation element N7 (third sun gear S3) and the tenth rotation element N10 (fourth sun gear S4), and is selectively connectable with the transmission housing H, thereby selectively acting as a fixed element.

The sixth connecting member TM6 interconnects the eighth rotation element N8 (third planet carrier PC3) and the twelfth rotation element N12 (fourth ring gear R4), and is externally gear-meshed with the input shaft IS selectively, thereby selectively acting as an input element.

The seventh connecting member TM7 is connected with the ninth rotation element N9 (third ring gear R3), and externally gear-meshed with the second connecting member TM2.

The eighth connecting member TM8 is connected with the eleventh rotation element N11 (fourth planet carrier PC4), and directly connected with the output shaft OS, thereby continuously acting as an output element.

The first transfer gear TF1 delivers a shifted torque of the main shifting portion having the first and second planetary gear sets PG1 and PG2 to the auxiliary shifting portion having the third, fourth planetary gear set PG3 and PG4, in a reverse rotation. The two transfer gears TF1 and TF2 delivers a shifted torque of the main shifting portion having the first, second, and third planetary gear sets PG1, PG2, and PG3 to the auxiliary shifting portion having the fourth planetary gear set PG4, in a reverse rotation.

The first transfer gear TF1 includes a first transfer drive gear TF1 a directly connected with the second connecting member TM2 and a first transfer driven gear TF1 b directly connected with the seventh connecting member TM7, and externally gear-meshes the second connecting member TM2 and the seventh connecting member TM7.

The second transfer gear TF2 delivers a torque of the input shaft IS to the auxiliary shifting portion having the third, fourth planetary gear set PG3 and PG4, in a reverse rotation.

The second transfer gear TF2 includes a second transfer drive gear TF2 a directly connected with the input shaft IS and a second transfer driven gear TF2 b directly connected with the sixth connecting member TM6, and externally gear-meshes the input shaft IS and the sixth connecting member TM6 selectively.

As a result, respective connecting members connected by the first and second transfer gears TF1 and TF2 rotate in opposite directions, and the gear ratios of the first and second transfer gears TF1 and TF2 may be preset in consideration of required speed ratio of the transmission.

The control elements include the three clutches C1, C2, and C3 and the three brakes B1, B2, and B3 are arranged as follows.

The first clutch C1 is arranged between the input shaft IS and the first connecting member TM1, such that a torque of the input shaft IS may be selectively transmitted to the first connecting member TM1.

The second clutch C2 is arranged between the second transfer gear TF2 and the sixth connecting member TM6 is arranged between such that a torque of the input shaft IS may be selectively transmitted to the sixth connecting member TM6.

The third clutch C3 is arranged between the input shaft IS and the third connecting member TM3 such that a torque of the input shaft IS may be selectively transmitted to the third connecting member TM3.

The first brake B1 is arranged between the first connecting member TM1 and the transmission housing H, such that the first connecting member TM1 may selectively act as a fixed element.

The second brake B2 is arranged between the fourth connecting member TM4 and the transmission housing H, such that the fourth connecting member TM4 may selectively act as a fixed element.

The third brake B3 is arranged between the fifth connecting member TM5 and the transmission housing H, such that the fifth connecting member TM5 may selectively act as a fixed element.

The control elements of the first, second, and third clutches C1, C2, and C3 and the first, second, and third brakes B1, B2, and B3 may be realized as multi-plate hydraulic pressure friction devices that are frictionally engaged by hydraulic pressure.

FIG. 2 is an operational chart for respective control elements at respective shift-stages in a planetary gear train according to various embodiments of the present invention.

Referring to FIG. 2, a planetary gear train according to various embodiments of the present invention realizes shifting by operating three control elements among the three clutches C1, C2, and C3 and the three brakes B1, B2, and B3.

[The Forward First Speed]

In the forward first speed shift-stage D1, the third clutch C3 and the second and third brakes B2 and B3 are operated.

As a result, the third connecting member TM3 is connected with the input shaft IS by the operation of the third clutch C3. In this state, the torque of the input shaft IS is input to the third connecting member TM3, and the fourth connecting member TM4 and the fifth connecting member TM5 act as fixed elements by the operation of the second brake B2 and the third brake B3, thereby realizing the forward first speed by cooperative operation of respective connecting members and outputting a shifted torque to the output shaft OS connected with the eighth connecting member TM8.

[The Forward Second Speed]

In the forward second speed shift-stage D2, the third clutch C3 and the first and third brakes B1 and B3 are operated.

As a result, the third connecting member TM3 is connected with the input shaft IS by the operation of the third clutch C3. In this state, the torque of the input shaft IS is input to the third connecting member TM3, and the first connecting member TM1 and the fifth connecting member TM5 act as fixed elements by the operation of the first brake B1 and the third brake B3, thereby realizing the forward second speed by cooperative operation of respective connecting members and outputting a shifted torque to the output shaft OS connected with the eighth connecting member TM8.

[The Forward Third Speed]

In the forward third speed shift-stage D3, the first and third clutches C1 and C3 and the third brake B3 are operated.

As a result, the first connecting member C1 is connected with the input shaft IS by the operation of the first clutch C1, and the third connecting member TM3 is connected with the input shaft IS by the operation of the third clutch C3. In this state, a torque of the input shaft IS is simultaneously input to the first, third connecting member TM1 and TM3, and the fifth connecting member TM5 acts as a fixed element by the operation of the third brake B3, thereby realizing the forward third speed by cooperative operation of respective connecting members and outputting a shifted torque to the output shaft OS connected with the eighth connecting member TM8.

[The Forward Fourth Speed]

In the forward fourth speed shift-stage D4, the second and third clutches C2 and C3 and the third brake B3 are operated.

As a result, the sixth connecting member TM6 is externally gear-meshed with the input shaft IS by the operation of the second clutch C2, and the third connecting member TM3 is connected with the input shaft IS by the operation of the third clutch C3. In this state, a torque of the input shaft IS is simultaneously input to the third, sixth connecting member TM3 and TM6, and the fifth connecting member TM5 acts as a fixed element by the operation of the third brake B3, thereby realizing the forward fourth speed by cooperative operation of respective connecting members and outputting a shifted torque to the output shaft OS connected with the eighth connecting member TM8.

[The Forward Fifth Speed]

In the forward fifth speed shift-stage D5, the first, second, and third clutches C1, C2, and C3 are operated.

As a result, the first connecting member C1 is connected with the input shaft IS by the operation of the first clutch C1, the third connecting member TM3 is connected with the input shaft IS by the operation of the third clutch C3, and the input shaft IS is externally gear-meshed with the sixth connecting member TM6 by the operation of the second clutch C2. In this state, a torque of the input shaft IS is simultaneously input to the first, third, sixth connecting member TM1, TM3, and TM6, thereby realizing the forward fifth speed by cooperative operation of respective connecting members and outputting a shifted torque to the output shaft OS connected with the eighth connecting member TM8.

[The Forward Sixth Speed]

In the forward sixth speed shift-stage D6, the second and third clutches C2 and C3 and the first brake B1 are operated.

As a result, the sixth connecting member TM6 is connected with the input shaft IS by the operation of the second clutch C2, and the third connecting member TM3 is connected with the input shaft IS by the operation of the third clutch C3. In this state, a torque of the input shaft IS is input to the third connecting member TM3 and the sixth connecting member TM6, and the first connecting member TM1 acts as a fixed element by the operation of the first brake B1, thereby realizing the forward sixth speed by cooperative operation of respective connecting members and outputting a shifted torque to the output shaft OS connected with the eighth connecting member TM8.

[The Forward Seventh Speed]

In the forward seventh speed shift-stage D7, the second and third clutches C2 and C3 and the second brake B2 are operated.

As a result, the sixth connecting member TM6 is externally gear-meshed with the input shaft IS by the operation of the second clutch C2, and the third connecting member TM3 is connected with the input shaft IS by the operation of the third clutch C3. In this state, a torque of the input shaft IS is input to the third connecting member TM3 and the sixth connecting member TM6, and the fourth connecting member TM4 acts as a fixed element by the operation of the second brake B2, thereby realizing the forward seventh speed by cooperative operation of respective connecting members and outputting a shifted torque to the output shaft OS connected with the eighth connecting member TM8.

[The Forward Eighth Speed]

In the forward eighth speed shift-stage D8, the second clutch C2 and the first and second brakes B1 and B2 are operated.

As a result, the sixth connecting member TM6 is externally gear-meshed with the input shaft IS by the operation of the second clutch C2. In this state, the torque of the input shaft IS is input to the sixth connecting member TM6, and the first connecting member TM1 and the fourth connecting member TM4 act as fixed elements by the operation of the first brake B1 and the second brake B2, thereby realizing the forward eighth speed by cooperative operation of respective connecting members and outputting a shifted torque to the output shaft OS connected with the eighth connecting member TM8.

[The Forward Ninth Speed]

In the forward ninth speed shift-stage D9, the first and second clutch C1 and C2 and the second brake B2 are operated.

As a result, the first connecting member TM1 is connected with the input shaft IS by the operation of the first clutch C1, and the sixth connecting member TM6 is externally gear-meshed with the input shaft IS by the operation of the second clutch C2. In this state, a torque of the input shaft IS is input to the first connecting member TM1 and the sixth connecting member TM6, and the fourth connecting member TM4 acts as a fixed element by the operation of the second brake B2, thereby realizing the forward ninth speed by cooperative operation of respective connecting members and outputting a shifted torque to the output shaft OS connected with the eighth connecting member TM8.

[The Reverse Speed]

In the reverse speed REV, the first clutch C1 and second and third brakes B2 and B3 are operated.

As a result, the first connecting member TM1 is connected with the input shaft IS by the operation of the first clutch C1. In this state, the torque of the input shaft IS is input to the first connecting member TM1, and the fourth connecting member TM4 and the fifth connecting member TM5 act as fixed elements by the operation of the second brake B2 and the third brake B3, thereby realizing the reverse speed by cooperative operation of the connecting members and outputting a shifted torque to the output shaft OS connected with the eighth connecting member TM8.

FIG. 2 shows gear ratios calculated under the condition that the gear ratio of the first ring gear R1/the first sun gear S1 is 1.93, the gear ratio of the second ring gear R2/the second sun gear S2 is 1.56, the gear ratio of the third ring gear R3/the third sun gear S3 is 2.17, the gear ratio of the fourth ring gear R4/the fourth sun gear S4 is 2.20, the gear ratio of the first transfer driven gear TF1 b/the first transfer drive gear TF1 a is 1.08, and the gear ratio of the second transfer driven gear TF2 b/the second transfer drive gear TF2 a is 1.14.

FIG. 3 is a schematic diagram of a planetary gear train according to various embodiments of the present invention.

In a planetary gear train according to the various embodiments of FIG. 1, the second clutch C2 is arranged between the sixth connecting member TM6 and the second transfer gear TF2, as shown in FIG. 1. However, referring to FIG. 3, the second clutch C2 is arranged between the input shaft IS and the second transfer gear TF2 in a planetary gear train.

As a result, the various embodiments of FIG. 3 merely differ from the various embodiments of FIG. 1 in a location of the second clutch C2, but also selectively transmits a torque of the input shaft IS to the sixth connecting member TM6, which is not described in further detail.

FIG. 4 is a schematic diagram of a planetary gear train according to various embodiments of the present invention.

In a planetary gear train according to the various embodiments of FIG. 3, the first planetary gear set PG1 is arranged toward an engine side on the input shaft IS and the second planetary gear set PG2 is arranged toward an opposite side of the engine on the input shaft IS. However, referring to FIG. 4, the second planetary gear set PG2 is arranged toward an engine side on the input shaft IS and the first planetary gear set PG1 is arranged toward an opposite side of the engine on the input shaft IS.

As a result, only locations of the control elements of the first and third clutches C1 and C3 and first and second brakes B1 and B2 related to the first and second planetary gear sets PG1 and PG2 are different but operation and function is the same, which is therefore not described in further detail.

As described above, according to a planetary gear train of various embodiments of the present invention, at least eight forward speeds and at least one reverse speed may be realized by a combination of four planetary gear sets, two transfer gears, and five control elements, thereby providing improvement of power delivery performance and fuel consumption and improving installability by shortening the length of an automatic transmission.

In addition, according to a planetary gear train of various embodiments of the present invention, two transfer gears of external gears arranged on the output shaft OS are employed in addition to three planetary gear sets, and thus, gear teeth may be widely varied so as to easily achieve optimum gear ratio and to easily comply with required performance for respective vehicles.

Furthermore, according to a planetary gear train of various embodiments of the present invention, a gear ratio span of more than 11.0 may be achieved while realizing at least nine forward speeds and at least one reverse speed, thereby maximizing an engine driving efficiency.

Additionally, the linearity of step ratios of shift stages is secured while multi-staging the shift stages with high efficiency, thereby making it possible to improve drivability such as acceleration before and after a shift, an engine speed rhythmic sense, and the like.

For convenience in explanation and accurate definition in the appended claims, the terms “upper”, “lower”, “inner” and “outer”, “up,” “down,” “upper”, “lower,” “upwards,” “downwards”, “front”, “rear”, “back”, “inside”, “outside”, “inwardly,” “outwardly,” “interior”, “exterior”, “inner,” “outer”, “forwards” and “backwards” are used to describe features of the exemplary embodiments with reference to the positions of such features as displayed in the figures.

The foregoing descriptions of specific exemplary embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teachings. The exemplary embodiments were chosen and described in order to explain certain principles of the invention and their practical application, to thereby enable others skilled in the art to make and utilize various exemplary embodiments of the present invention, as well as various alternatives and modifications thereof. It is intended that the scope of the invention be defined by the Claims appended hereto and their equivalents. 

What is claimed is:
 1. A planetary gear train of an automatic transmission for a vehicle, comprising: a first planetary gear set including a first rotation element, a second rotation element, and a third rotation element; a second planetary gear set including a fourth rotation element, a fifth rotation element, and a sixth rotation element; a third planetary gear set including a seventh rotation element, an eighth rotation element, and a ninth rotation element; a fourth planetary gear set including a tenth rotation element, an eleventh rotation element, and a twelfth rotation element; an input shaft mounted with the first and second planetary gear sets at an external circumference of the input shaft; an output shaft disposed in parallel with the input shaft and mounted with the third and fourth planetary gear set on external circumference of the output shaft; a first connecting member connected with the first rotation element; a second connecting member interconnecting the second rotation element and the fifth rotation element; a third connecting member interconnecting the third rotation element and the fourth rotation element; a fourth connecting member connected with the sixth rotation element; a fifth connecting member interconnecting the seventh rotation element and the tenth rotation element; a sixth connecting member connecting the eighth rotation element and the twelfth rotation element and connected to the input shaft selectively; a seventh connecting member connected with the ninth rotation element and engaged with the second connecting member; an eighth connecting member connected with the eleventh rotation element and directly connected with the output shaft; and transfer gears connected with at least two of the first, second, third, fourth, fifth, sixth, seventh, and eighth connecting members.
 2. The planetary gear train of claim 1, wherein the first connecting member is selectively connectable with at least one of the input shaft and a transmission housing; the third connecting member is selectively connectable with the input shaft; the fourth connecting member is selectively connectable with the transmission housing; and the fifth connecting member is selectively connectable with the transmission housing.
 3. The planetary gear train of claim 1, wherein the first planetary gear set comprises a first sun gear as the first rotation element, a first planet carrier as the second rotation element, and a first ring gear as the third rotation element; the second planetary gear set comprises a second sun gear as the fourth rotation element, a second planet carrier as the fifth rotation element, and a second ring gear as the sixth rotation element; the third planetary gear set comprises a third sun gear as the seventh rotation element, a third planet carrier as the eighth rotation element, and a third ring gear as the ninth rotation element; and the fourth planetary gear set comprises a fourth sun gear as the tenth rotation element, a fourth planet carrier as the eleventh rotation element, and a fourth ring gear as the twelfth rotation element.
 4. The planetary gear train of claim 1, wherein on the input shaft, the first planetary gear set is disposed toward an engine side and the second planetary gear set is disposed at an opposite side to the first planetary gear set; and on the output shaft, the fourth planetary gear set is disposed toward an engine side and the third planetary gear set is disposed at an opposite side to the fourth planetary gear set.
 5. The planetary gear train of claim 1, wherein on the input shaft, the second planetary gear set is disposed toward an engine side and the first planetary gear set is disposed at an opposite side to the second planetary gear set; and on the output shaft, the fourth planetary gear set is disposed toward an engine side and the third planetary gear set is disposed at an opposite side to the fourth planetary gear set.
 6. The planetary gear train of claim 1, wherein the transfer gears comprise: a first transfer gear disposed between the second connecting member and the seventh connecting member; and a second transfer gear disposed between the input shaft and the sixth connecting member.
 7. The planetary gear train of claim 6, further comprising: a first clutch disposed between the input shaft and the first connecting member; a second clutch disposed between the second transfer gear and the sixth connecting member; a third clutch disposed between the input shaft and the third connecting member; a first brake disposed between the first connecting member and a transmission housing; a second brake disposed between the fourth connecting member and the transmission housing; and a third brake disposed between the fifth connecting member and the transmission housing.
 8. The planetary gear train of claim 6, further comprising: a first clutch disposed between the input shaft and the first connecting member; a second clutch disposed between the input shaft and the second transfer gear; a third clutch disposed between the input shaft and the third connecting member; a first brake disposed between the first connecting member and the transmission housing; a second brake disposed between the fourth connecting member and a transmission housing; and a third brake disposed between the fifth connecting member and the transmission housing.
 9. A planetary gear train of an automatic transmission for a vehicle, comprising: a first planetary gear set including a first rotation element, a second rotation element, and a third rotation element; a second planetary gear set including a fourth rotation element, a fifth rotation element, and a sixth rotation element; a third planetary gear set including a seventh rotation element, an eighth rotation element, and a ninth rotation element; a fourth planetary gear set including a tenth rotation element, an eleventh rotation element, and a twelfth rotation element; an input shaft mounted with the first and second planetary gear sets at an external circumference of the input shaft; and an output shaft disposed in parallel with the input shaft and mounted with the third and fourth planetary gear sets on an external circumference of the output shaft, wherein the first rotation element is selectively connectable with at least one of the input shaft and a transmission housing, the second rotation element is directly connected with the fifth rotation element, the third and fourth rotation elements are directly connected to each other and selectively connectable with the input shaft, the seventh and tenth rotation elements are directly connected to each other and selectively connectable with the transmission housing, the eighth and twelfth rotation elements are directly connected to each other and connected with the input shaft selectively, the ninth rotation element is connected with the fifth rotation element, and the eleventh rotation element is directly connected with the output shaft.
 10. The planetary gear train of claim 9, wherein the first planetary gear set comprises a first sun gear as the first rotation element, a first planet carrier as the second rotation element, and a first ring gear as the third rotation element; the second planetary gear set comprises a second sun gear as the fourth rotation element, a second planet carrier as the fifth rotation element, and a second ring gear as the sixth rotation element; the third planetary gear set comprises a third sun gear as the seventh rotation element, a third planet carrier as the eighth rotation element, and a third ring gear as the ninth rotation element; and the fourth planetary gear set comprises a fourth sun gear as the tenth rotation element, a fourth planet carrier as the eleventh rotation element, and a fourth ring gear as the twelfth rotation element.
 11. The planetary gear train of claim 9, wherein on the input shaft, the first planetary gear set is disposed toward an engine side and the second planetary gear set is disposed to an opposite side of the engine side; and on the output shaft, the fourth planetary gear set is disposed toward an engine side and the third planetary gear set is disposed to an opposite side of the engine side.
 12. The planetary gear train of claim 9, wherein on the input shaft, the second planetary gear set is disposed toward an engine side and the first planetary gear set is disposed to an opposite side of the engine side; and on the output shaft, the fourth planetary gear set is disposed toward an engine side and the third planetary gear set is disposed to an opposite side of the engine side.
 13. The planetary gear train of claim 9, wherein the fifth rotation element is connected with the ninth rotation element through a first transfer gear, and the input shaft is connected with the twelfth rotation element selectively through a second transfer gear.
 14. The planetary gear train of claim 13, further comprising: a first clutch selectively connecting the input shaft and the first rotation element; a second clutch selectively connecting the second transfer gear and the twelfth rotation element; a third clutch selectively connecting the input shaft and the fourth rotation element; a first brake selectively connecting the first rotation element to the transmission housing; a second brake selectively connecting the sixth rotation element to the transmission housing; and a third brake selectively connecting the seventh rotation element to the transmission housing.
 15. The planetary gear train of claim 13, further comprising: a first clutch selectively connecting the input shaft and the first rotation element; a second clutch selectively connecting the input shaft and the second transfer gear; a third clutch selectively connecting the input shaft and the fourth rotation element; a first brake selectively connecting the first rotation element to the transmission housing; a second brake selectively connecting the sixth rotation element to the transmission housing; and a third brake selectively connecting the seventh rotation element to the transmission housing. 